1. Field of the Invention
The present invention relates to flat panel displays generally, and more particularly, to an electroluminescent (EL) display device having a structure that prevents an emission portion from being damaged during fabrication.
2. Description of the Related Art
Flat panel displays, such as liquid crystal displays (LCDs) or organic or inorganic electro-luminescent (EL) displays, may be either a passive matrix (PM) type or active matrix (AM) type depending on the driving method employed. In a PM type flat panel display, a plurality of anodes are arranged in columns and a plurality of cathodes are arranged in rows. In operation, a row driving circuit transmits a scan signal to a single cathode selected from a row. Similarly, a column driving circuit transmits a data signal to a pixel selected from a row.
AM type flat panel display is widely used as a device for displaying moving pictures since it efficiently processes high bandwidth signals by using a thin film transistor (TFT) to control the signal input to each pixel.
An organic EL display sandwiches an organic emission layer between an anode and a cathode. When an anode voltage and a cathode voltage are applied to the anode and the cathode, respectively, holes introduced from the anode are transported to the emission layer via a hole transport layer, and electrons introduced from the cathode are transported to the emission layer via an electron transport layer. In the emission layer, the electrons and the holes recombine to produce excitons. As the excited state of the excitons changes to a ground state, fluorescent molecules on the emission layer emit light to form an image. Full-color organic EL displays include pixels emitting three colors, red (R), green (G), and blue (B).
For EL displays generally, and organic EL displays particularly, longevity of the display depends on keeping an organic emission portion of a display region as free from moisture as possible.
Various conventional methods and apparatuses have attempted to provide a moisture-proof solution. One such method disclosed in Korean Patent Laid-open Publication No. 2002-0065125 applies an ultraviolet (UV)-curing sealant to the edge of an emission substrate, assembles the emission substrate to a seal substrate, and cures the sealant with UV rays. The energy of the UV rays may however permeate an organic emission portion. During the sealing of the organic emission portion, however, such energy may transmit through an upper layer formed on the organic emission portion and damage the organic emission portion.
Another technique disclosed in Korean Patent Laid-open Publication No. 2000-0065694 interposes a LiF layer between a cathode and an emission layer to improve color efficiency. A similar approach was adopted in Japanese Patent Laid-open Publication No. 2000-200683, which interposes a LiF layer as an electron injection layer (EIL) between a cathode and an organic layer.
In both cases, the LiF layer is limited in thickness. Accordingly, the LiF layer cannot effectively protect the organic emission portion from external energy, such as UV rays. Accordingly, a solution is needed that provides a moisture-proof emission layer and a method of manufacturing the same that minimizes or prevents damage to the emission layer during manufacture.